Papers and Research ToC

Table of Contents

1. Biology
1. Pseudoephedrine Cochrane Review
2. Ethics
1. Ethical Motivation for Sustainability
2. Sustainability Agenda
3. Sustainability Beta Test
4. Obstacles of Sustainability
5. Rational Decision Making
3. Physics
1. Magnetic Fields in Star Formation
2. Pulsar Formation and Structure
3. Discovery of a Very Low Mass Triple with Late-M and T Dwarf Components: LP 704-48/SDSS J0006-0852AB
4. A Search for Photometric Variability in L and T type Brown Dwarf Atmospheres
4. Self-Improvement
1. Skill Acquisition

Notes - Reference Models

The following are notes from Computer Networks written by Tanenbaum 5th edition.

• layered networks in the abstract
• TCP/IP reference model

The OSI Reference Model

• OSI modle minus physical medium is based on proposal developed by ISO (International Standards Organization)
• OSI model
• seven layers
• a layer should be created where a different abstraction is needed
• each layer should perform a well defined function
• function should be chosen to define international standards
• layer boundaries chosen to minimize information flow across interfaces
• number of layers large enough that distinct functions don't need to be thrown together in same layer, small enough that architecture isn't unwieldy
• Physical Layer
• transmit of raw bits over communication channel
• 1,0 bit communication
• electrical signals, how connection established, how connections torn down
• pins network connector has
• mechanical electrical and timing interfaces
• Data Link Layer
• raw transmission into a line free of undetected transmission errors
• mask real errors so network layer doesn't see them
• data frames
• send back acknowledgement frame
• special sublayer of data link layer
• MAC (Medium Access Control) sublayer
• Network Layer
• controls operation of subnet
• determine how packets are routed from source to destination
• routes based on tables, updatable to reflect machines
• handling congestion
• quality of service
• delay
• transmit time
• jitter
• broadcast networks, routing is simple so this layer is thin for that system
• Transport Layer
• Accept data from above it
• split into smaller units
• determines type of service to provide to session layer
• error free point to point channel is most popular
• type of service determined when connection established
• end to end layer, carries data from source to destination
• Session Layer
• establish sessions
• dialog control keep track of whose turn it is to transmit
• token management prevent parties from attempting same operatio simultaneously
• synchronization
• Presentation layer
• concerned with syntax and semantics of information transmitted
• manages abstract data structures
• allows for higher level data structures to be defined
• Application Layer
• HTTP(hyper text transfer protocol)
• variety of protocols for users
• e-mail, file transfer, network news

The TCP/IP Reference Model

• TCP/IP used in ARPANET
• ARPANET was a research network sponsored by the department of defense
• used to connect multiple networks seamlessly
• survive loss of subnet hardware
• survive as long as source/destination functioning
• The Link Layer
• packet switching network
• serial lines
• interface between hosts and transmission links
• Internet Layer
• corresponds roughly to OSI Network layer
• permit hosts to inject packets into any network and travel independently to destination
• may arrive out of order
• snail mail equivalent
• defines official packet format and protocol called IP(Internet Protocol)
• ICMP(Internet Control Message Protocol)
• helps function
• Transport Layer
• layer above the internet layer in TCP/IP
• allow peer entities on source and destination to carry out a conversation
• two end to end transport protocols have been defined here
• TCP
• Transmission Control Protocol
• connection oriented
• byte stream delivered without error to other machine
• reassembles received messages into output stream
• UDP
• User Datagram Protocol
• unreliable connectionless protocol
• one shot client server request reply queries
• used for prompt delivery over accuracy
• speech or video
• The Application Layer
• does not have session or presentation layers
• applications includes the above
• all higher level protocols
• TELNET
• virtual terminal
• FTP
• File transfer protocol
• SMTP
• simple mail protocol

The Model Used in This Book

• OSI strength is the model itself used for discussion
• TCP/IP is used as the protocols
• hybrid scheme
• Application
• contains programs
• Transport
• transmit
• Network
• how to combine multiple links into networks
• how to find paths
• Link
• how to send finite length messages
• Physical
• how to transmit bits

A Comparison of the OSI and TCP/IP Reference Models

• Both are based on the concept of a stack of independent protocols
• functionality roughly similar
• OSI
• differentiation is explicit
• Services
• performs services for layer above it
• defines semantics
• Interfaces
• tells process how to access
• Protocols
• used in a layer and is the layer's own business
• fits with object oriented style programming
• devised before protocols invented, so extremely general
• convergence sublayers have to be grafted on to account for network differences
• supports connection oriented/connectionless
• TCP/IP
• does not distinguish
• have been modeled to make it similar to OSI
• protocols came first model defined afterwards, easy fit
• not useful in describing non TCP/IP networks
• supports connectionless in network, both in transport layer

A Critique of the OSI Model and Protocols

• Bad Timing
• time of standardization is crucial
• in between research and investment
• TCP/IP already in use by universities by the time OSI appeared
• universities/companies did not want to support
• Bad Technology
• model and protocols are flawed
• very complex
• functions repeated
• Bad Implementation
• complexity means implementations large unwieldy and slow
• OSI associated with poor quality
• TCP/IP was good and free from Berkeley, large user communities/improvements
• Bad Politics
• TCP/IP was seen as part of UNIX
• OSI seen as government control

A Critique of the TCP/IP Reference Model

• Models don't distinguish specifications/implementations
• not much of a guide for design
• not general
• link layer is not really a layer, just an interface
• does not distinguish physical and data layers
• Many protocols ad hoc and distributed free
• TELNET designed for 10 character per second mechanical teletype terminal no gui or mice

Back to ToC

Trivia - A Google a Day XLVIII

On December 1, 2008, whom did president-elect Obama nominate to become his Secretary of State?
Hilary Clinton

What role did Judy Tyler play on the popular NBC kids' show set in Doodyville?
Princess Winterfall Summerspring

What is the name of the bridge that takes Ohio State Route 261 over the Little Cuyahoga River?
All-American Bridge

What insect prefers the Mengaris tree because of its slippery trunk and high branches, making it difficult for its natural predator, the Helarctos malayanus, to get to it?
Asian Rock Bees

What was the cultural movement that started around 1919 and extended into the early 1930s in which African-American literature and art flourished in New York City?
Harlem Renaissance

What is the capital of the country that was home to the Norte Chico civilization, as well as the Inca Empire?
Lima

What does Douglas Adams cite as the reason for people's unhappiness in the preface to his 1979 absurdist novel?
Money

What product from a San Francisco company involves an animal figurine made of clay on which dampened Salvia Columbariae are placed?
Chia Pet

In what county of Ireland is the megalithic complex set between Macroom and Millstreet near Musherabeg mountain?
Cork

What lies beneath the fish and connects it to the ram in the Northern Hemisphere constellations?
Cetus

Tanenbaum Computer Networks ToC

Table of Contents

The following is a table of contents for notes from Tanenbaum's Computer Networks

1. Introduction
1. Uses of Computer Networks
2. Network Hardware
3. Network Software
4. Reference Models
5. Example Networks
6. Network Standardization
7. Metric Units
2. The Physical Layer
1. The Theoretical Basis For Data Communication
2. Guided Transmission Media
3. Wireless Transmission
4. Communication Satellites
5. Digital Modulation and Multiplexing
6. The Public Switched Telephone Network
7. The Mobile Telephone System
8. Cable Television
3. The Data Link Layer
1. Data Link Layer Design issues
2. Error Detection and Correction
3. Elementary Data Link Protocol
4. Sliding Window Protocols
5. Example Data Link Protocols
4. The Medium Access Control Sublayer
1. The Channel Allocation Problem
2. Multiple Access Protocol
3. Ethernet
4. Wireless LANs
5. Broadband Wireless
6. Bluetooth
7. RFID
8. Data Link Layer Switching
5. The Network Layer
1. Network Layer Design Issues
2. Routing Algorithm
3. Congestion Control Algorithms
4. Quality of Service
5. Internetworking
6. The Network Layer in the Internet
6. The Transport Layer
1. The Transport Service
2. Elements of Transport Protocols
3. Congestion Control
4. The Internet Transport Protocols: UDP
5. The Internet Transport Protocols: TCP
6. Performance Issues
7. Delay-Tolerant Networking
7. The Application Layer
8. Network Security
9. Glossary

Notes - Network Software

The following are notes from Computer Networks written by Tanenbaum 5th edition.

• First networks were designed with hardware as the main concern, and software as an afterthought, but this is no longer the case

Protocol Hierarchies

• Networks are organized as a stack of layers/levels
• purpose of each layer is to 
• offer services to higher layers
• shield details in implementation from higher layers
• Protocol
• agreement between communication parties on how to proceed
• violating protocol makes communications more difficult
• Peers
• Entities comprising corresponding layers on different machines
• can be software, hardware, or humans
• peers communicate using protocol
• no data is directly transferred from layer n on one machine to layer n on another
• data passes to layer below it until lowest layer is reached
• transfer through physical communication

• between adjacent layers is an interface
• layer must perform specific collection of well understood functions
• protocols within a layer can change without layers above and below noticing
• Network Architecture
• set of layers and protocols
• contain enough information to allow implementer to write or build hardware to obey correct protocols
• interfaces are the same on all machines in a network, not visible from outside
• Protocol stack
• list of protocols used by a system
• example
• Message M produced by application process layer 5
• given to layer 4 to transmission
• pust a header in front to identify the message
• header includes control information, such as addresses
• usually no limit on size of transmission
• pass to layer 3
• breaks up messages into units and packets
• prepends layer 3 header to each packet
• decides outgoing lines to use
• pass to layer 2
• adds a trailer to each piece
• pass to layer 1
• physical transmission
• received message goes up in layers
• peer processes
• from same layer to same layer communication, even though the message passes through lower layers

Design Issues for the Layers

• Reliability is the design issue of making correctly operating network
• codes for error detection
• more powerful codes allow for error correction
• finding working path
• routing
• evolution of network
• protocol layering
• addressing/naming to identify senders and receivers
• differences in max size of messages
• scalability
• resource allocation
• Statistical multiplexing
• sharing based on statistics of demand
• flow control
• oversubscribed to a channel, network cannot deliver
• congestion
• real time delivery high throughput
• quality of service
• Security
• confidentiality to defend against eavesdropping on layers
• authentication to prevent impersonation
• integrity

Connection-Oriented Versus Connectionless Service

• Connection-oriented
• modeled after telephone system
• service first establishes connection
• uses connection then release
• order of bits/date preserved
• negotiation about parameters to be used
• makes proposal, other side, accept, reject, counterproposal
• circuit - connection with associated resources, such as fixed bandwidth
• Connectionless
• modeled after postal system
• full destination address
• routed through intermediate nodes
• packet is a message at network layer
• store and forward switching
• receive message in full before sending to next node
• cut-through switching
• transmission starts before completely received
• Both characterized by reliability
• connection oriented service
• file transfer
• all bits arrived correctly and in same order
• message sequences
• has boundaries preserved, message length same
• i.e. pages in a book
• byte streams
• no message boundary
• i.e. download movie
• voice over IP
• video conference
• few pixels wrong is ok, some noise ok better than having a delay
• unreliable connectionless service 
• datagram
• from telegram, does not return an acknowledgement or ack to sender
• dominant form in networks despite unreliability
• acknowledged datagram service
• send letter request return receipt
• request reply service
• datagram sends request, reply sends answer
• client-server implementation

Service Primitives

• primitives(operations)
• formally specified to access a service
• Socket interface
• LISTEN
• Block wait for incoming connection
• CONNECT
• establish connection
• ACCEPT
• accept connection
• RECEIVE
• wait for message
• SEND
• send message
• DISCONNECT
• terminate connection
• Server Client
• Server executes LISTEN to accept incoming connections
• Client executes CONNECT to establish connection with server
• Packet arrives at server, OS sees package is requesting connection
• checks for listener
• Server executes CONNECT
• sends response to client
• on arrival client released
• both sides are running and have connection
• Server executes RECEIVE
• accept first request
• after release from listen goes into this phase
• Client executes SEND
• immediately after SEND goes into RECEIVE
• to get reply
• arrival of request unblocks server to handle request
• Server executes SEND
• arrival of packet unblocks client
• Client done
• call DISCONNECT
• sends packet to server saying connection not needed
• Server DISCONNECT
• 6 packets required to complete protocol

Relationship of Services to Protocols

• Services and Protocols distinct
• service is a set of primitives to layer above it
• defines operations to be performed
• relates to an interface between two layers
• protocol set of rules governing format and meaning of packets
• service definitions
• can change protocols at will as long as service visible not changed
• like abstract data type

Back to ToC

Notes - Network Hardware

The following are notes from Computer Networks written by Tanenbaum 5th edition.

• There are two types of transmission technology in wide use
• broadcast links
• shared by all machines on network
• one machine sends to all machines, address in packet specifies recipient
• can address to all instead of specified machine
• multicasting
• point to point links
• connect individual pairs of machines
• transmit packets, short messages from one to another
• packet may visit multiple machines before arrival
• one sender one receiver called unicasting
• Classify Networks by scale, distance is important,
• 1m - personal area network
• 10 m -> 1km - local area network
• 10km - Metropolitan area network
• 100km-100km - Wide area network
• 10,000km - Internet (Planet wide)

Personal Area Networks

• PANs(Personal area Networks)
• computer to peripherals
• mouse
• keyboard
• monitor
• Bluetooth
• wireless connections
• i.e. music player connects to car
• Master-slave paradigm
• system unit (PC) is master
• master tells slaves 
• what addresses to use
• when to broadcast
• length of transmission
• frequency used
• Pacemakers and other medical devices
• user operated remote control

Local Area Networks

• LAN(Local Area Network)
• Privately owned network
• connects personal computers and consumer electronics
• used by companies - Enterprise Networks
• (AP)Access Point
• wireless router
• base station
• relays packets between computers and internet
• IEEE 802.11
• Wi Fi
• 11 - 100s Mbps
• Wired Lans
• Ethernet, built from point to point links
• switched ethernet
• computer speaks to internet protocol
• connects to a box called a switch with point to point links
• switch has multiple ports
• packet relay
• Build larger lans, switches plugged into each other using ports
• use protocols and path finding to reach destination
• Divide a large physical LAN into smaller logical lans
• VLAN (Virtual Lan)
• each port is tagged with "color"
• color is a subgroup of LAN
• i.e. red for finance, green for engineering, broadcast on red will not be seen on green
• classic Ethernet
• broadcast over cables
• Broadcast Networks can be divided into static and dynamic designs based on channel allocation
• Centralized, single entity, base station decides priority in sending
• decentralized each machine decides when and how to send
• Home Networks
• Networked devices have to be easy to install
• foolproof in operation
• due to low consumer tolerance
• low price
• expand reach of network
• security
• Power-line networks
• broadcast from devices that plug into outlets

Metropolitan Area Networks

• MAN(Metropolitan Area Network)
• covers a city
• i.e. cable television networks
• At first these were local ad hoc systems
• Internet caused changes to cable TV network, instead of distribution became MAN
• cable headend
• feed in television signal
• internet
• WiMAX
• IEEE 802.16

Wide Area Networks

• WAN(Wide Area Network)
• large geographic area
• i.e. country/continent
• Composed of
• Transmission lines - to move bits between machines
• Switching elements - computers that connect two or more transmission lines
• aka router
• Offices contain host computers
• connection of hosts is subnet
• carries messages from host to host
• originally only meant collection of routers and lines
• now sometimes definition related to network addressing
• members can be
• individual computers
• LANs
• Owned by different people
• Routers connect different kinds of networking technology
• internetworks
• composite networks made up of more than one network
• VPN(Virtual Private Network)
• company connects offices through internet alone
• Network service provider
• subnet operator
• ISP(Internet Service Provider)
• ISP network
• Routing Algorithm
• how network makes decisions on which path to use
• Forwarding algorithm
• how router makes decision on where to send packet next
• WANs sometime use wireless technology heavily to satellites
• computers hear from satellites
• inherently broadcast
• i.e. cellphone
• first generation analog voice
• second generation digital for voice
• third generation is digital for voice and data

Internetworks

• Internet
• connection of different frequently incompatible networks
• uses ISP networks to connect private networks together
• gateways
• provides a translation for hardware and software between networks and protocols

Back to ToC

Trivia - A Google a Day XLVII

In what war was the automatic machine gun introduced?
WWI

What will you find at the end of Beach 47th Street in New York, New York?
Coney Island Lighthouse

What is the study of motion that, unlike dynamics, does not consider the influence of mass and force?
Kinematics

What is the title of the novella by Stephen King that tells the story of Red, who narrates the story, and Andy, both prison inmates?
Rita Hayworth and Shawshank Redemption

What university did the third president of the U.S. design, then used a telescope to supervise construction of it from his home on a hilltop above the campus?
University Of Virginia

How many stories (officially) is the structure located at 350 5th Avenue in New York City?
102

What crater on Mars measures the same distance across as the distance between Selby Botanical Gardens and the falls that divide the U.S. and Canada?
Hellas Basin

With what team did the Hall of Fame outfielder, who retired with 399 home runs, play his entire 22-season career?
Detroit Tigers

What was the name of Beatrix Potter's childhood rabbit that inspired the creation of "Peter Rabbit"?
Peter Piper

In the co-author's phantasmagoric addition to "Lyrical Ballads", where does the old sailor tell his story to the guest?
A Wedding